Aircraft in flight are commonly refueled from a refueling aircraft. The refueling aircraft is typically provided with a boom mechanism or a flexible hose which trails behind the aircraft and physically makes a connection to the aircraft to be refueled. Many refueling aircraft use a system of fixed and extendable metal tubing to provide the fluid connection for refueling an aircraft. For the tube type system, a fixed tube is normally attached to the aircraft and a distal end of the fixed tube provides for an extendable length of tubing. An operator in the refueling aircraft either visually or with the assistance of camera equipment can visually observe the extension of the tubing to align the tubing to the receiving aircraft.
The tube type refueling boom normally has steerable fins or ailerons attached at specific locations to allow the refueling operator to “fly” the refueling boom. Hydraulic controls allow the boom operator to therefore steer the boom towards the aircraft to be refueled.
Once the refueling boom is connected to the aircraft to be fueled, most tube type refueling booms in use do not provide for automatic boom load alleviation. Stresses are placed on a boom due to the motion of the refueling aircraft, as well as from the aircraft to be refueled. These stresses can result in boom failure. In these systems, the boom operator is responsible to continue to steer the boom during the refueling operation whenever the boom appears to be deflecting. A typical boom extends out between approximately 12.2 meters (m) to 15.2 m (40-50 feet) in its fully extended position. It is therefore difficult for the boom operator to visually detect a deflection at the end of the boom adjacent to the aircraft to be fueled. A drawback of manually steering the boom is that boom stresses can build up before the operator is aware of the boom deflection.
A boom load alleviation system employing strain gauges to identify the load on a boom in use is known. This load alleviation system relies on electrical feedback from the strain gauges to a computer onboard the aircraft which identifies a boom bending load. The strain gage signals are analyzed by the computer which provides automatic control to re-steer the boom back to a lower load position. The disadvantage of this strain gauge type load alleviation system is the expense of the equipment, the maintenance of the strain gauge equipment, and the potential for damage to the strain gages since the refueling boom adjacent to the strain gauge installation commonly contacts the aircraft to be refueled.
A need therefore exists for a simplified boom load alleviation system which provides a simpler, less expensive, and more durable system.